1. Field of the Invention
This invention relates to a process for producing vitamin A or its carboxylic acid esters. Vitamin A or its carboxylic acid esters, typical of which are the acetate and palmitate, are used in large quantities as medicines, feed additives and the like.
2. Description of the Prior Art
For the production of vitamin A, there is known, as described in European Patent Publication No. 0 187 259, a process wherein halogenated sulfones are treated with bases in hydrocarbon solvent according to the following reaction sequence to obtain vitamin A. ##STR1##
According to the above known process, when a halogenated sulfone used as a starting material for the reaction is treated with a potassium alkoxide, vitamin A can be obtained in relatively high yield. However, the potassium alkoxide has the problem with respect to availability and cost, thus leaving much room for improvement.